There has been much research into effective introduction of nucleic acids into target cells and tissues for use in e.g. gene therapy. Such nucleic acids may be e.g. sequences encoding a gene product or instead short sequences of nucleotides that correspond to the sense or antisense sequence of specific genes or their products and hence have a direct effect on the expression of these genes and/or their products.
There continue to exist problems in delivering the nucleic acids to the correct target site and to a sufficient number of target cells. Nucleic acids are subject to nuclease attack and are often unable to cross cell membranes. A wide variety of delivery methods have been proposed, including microinjection, scrape loading, and receptor-mediated endocytosis. Lipid-based carrier systems, including those involving use of liposomes, are frequently used to package the therapeutic nucleic acids. However, the use of liposomes may pose problems such as poor encapsulation efficacy and rapid clearance from circulation. There may also be problems in packaging enough nucleic without increasing the size of the liposome to the point where delivery to the target tissues is impaired. Accordingly, there exists a need to develop liposome-based delivery systems for targeting nucleic acids to the correct target tissue.